HR: 0800h
AN: PP51C-0605    [Abstracts]
TI: The Laminated Marca Shale: High-Frequency Climate Cycles From the Latest Cretaceous
AU: * Davies, A
EM: adz@noc.soton.ac.uk
AF: National Oceanographic Centre, Southampton, School of Ocean & Earth Science University of Southampton Waterfront Campus European Way, Southampton, SO14 3ZH United Kingdom
AU: Kemp, A E
EM: aesk@noc.soton.ac.uk
AF: National Oceanographic Centre, Southampton, School of Ocean & Earth Science University of Southampton Waterfront Campus European Way, Southampton, SO14 3ZH United Kingdom
AU: Weedon, G
EM: g.p.weedon@swansea.ac.uk
AF: University of Wales, Swansea , Environmental Modelling and Earth Observation group, Department of Geography, Singleton Park, Swansea, SA2 8PP United Kingdom
AU: Barron, J A
EM: jbarron@usgs.gov
AF: U.S. Geological Survey, MS 910, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AB: The Latest Cretaceous (Maastrichtian) Marca Shale Member, California, displays a well-preserved record of alternating terrigenous and diatomaceous laminae couplets, remarkably similar in lithology to recent laminated sediments from the Gulf of California and Santa Barbara Basin. This similarity, together with the recognition of intra- and inter-annual variability in the diatom flora, implies an annual origin for these couplets. High-resolution backscattered electron imagery has identified two sublaminae types within the varved succession; near monospecific lamina of Chaetoceros-type resting spore and of large Azpeitiopsis morenoensis. The composition and occurrence of these laminae is similar to ENSO forced intra-annual variability of diatom flora along the modern Californian margin. Relative thickness variations in terrigenous and biogenic laminae (proxies for precipitation and productivity respectively) also exhibit similar characteristics to variability in Quaternary varves from the Santa Barbara Basin, shown to be imparted by ENSO forcing. In order to track changes in the levels of bottom water oxygenation within the basin, a bioturbation index was established. Periods when bioturbation was minimal (enhanced benthic anoxia) coincide with times of greatest diatomaceous export flux and also lowest flux of detrital material. Conversely, periods of enhanced bioturbation correspond with reduced diatomaceous export flux and an increased flux of detrital material, comparable with ENSO forced variations in diatomaceous and terrigenous export flux and associated benthic oxygenation levels in Pleistocene varves off the Californian margin. Power spectra obtained from time-series analysis of the bioturbation index and laminae thickness variations exhibit strong signals within the ENSO band. This research implies that high-frequency climate perturbations are inherent components of the climate system and that ENSO-type variability was not confined to the dynamic climate system of the Quaternary, but occurred as far back as the Cretaceous. These results also add to the growing body of evidence which indicate that warm end-member climate states are not characterised by a permanent El Nino state.
DE: 4922 El Nino (4522)
DE: 4944 Micropaleontology (0459, 3030)
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005